Long-term BVRI photometric light curves of 15 PMS stars in the IC 5070 star-forming region
Sunay Ibryamov, Evgeni Semkov, Teodor Milanov, Stoyanka Peneva
aa r X i v : . [ a s t r o - ph . S R ] M a y Research in Astronomy and Astrophysics manuscript no.(L A TEX: ms0085R1.tex; printed on May 31, 2018; 0:41)
Long-term
BV RI photometric light curves of 15 PMS stars inthe IC 5070 star-forming region ∗ Sunay Ibryamov , Evgeni Semkov , Teodor Milanov and Stoyanka Peneva Department of Physics and Astronomy, Faculty of Natural Sciences, University of Shumen, 115,Universitetska Str., 9700 Shumen, Bulgaria; [email protected] Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences, 72,Tsarigradsko Shose Blvd., 1784 Sofia, Bulgaria
Abstract
This paper reports the results from the multicolor photometric observations of15 pre-main sequence stars collected in the period 2010 September − BV RI photometric data allows to draw a conclusion thatall investigated objects are variable stars. In the case of LkH α
146 we identified previouslyunknown periodicity in its photometric variability.
Key words: stars: pre-main sequence — stars: variables: T Tauri, Herbig Ae/Be — stars:individual (LkH α α α α α α α α The North-America and Pelican nebulae (NGC 7000/IC 5070) represent one of the most notable and well-studied active star-forming complexes, where a large number of young pre-main sequence (PMS) stars,cometary nebulae, collimated jets and Herbig-Haro objects can be found (Herbig 1958, Guieu et al. 2009,Rebull et al. 2011 and Bally et al. 2014). Recent major studies of the NGC 7000/IC 5070 complex weremade by Rebull et al. (2011), Armond et al. (2011), Zhang et al. (2014), Bally et al. (2014) and Damiani etal. (2017). ∗ Based on observations obtained at the Rozhen National Astronomical Observatory, Bulgaria. The photometric data are onlyavailable at the CDS.
S. Ibryamov, E. Semkov, T. Milanov & S. Peneva
One of the most important features of PMS stars is their photometric and spectroscopic variabilitydiscovered at the beginning of their study. PMS stars are separated into two types − the low-mass T Tauristars (TTSs) and the more massive Herbig Ae/Be stars (HAEBESs). The TTSs exhibit strong irregularphotometric variability and emission spectra. TTSs are divided into two sub-classes − classical T Tauri stars(CTTSs), still actively accreting from their circumstellar disks, and the weak-line T Tauri stars (WTTSs)which show no signs of disk accretion (M´enard & Bertout 1999).The superpositions of cool and hot spots on the stellar surface; flare-like events; variable mass accretionrate from the circumstellar disk onto the stellar surface; as well as circumstellar dust or clouds obscurationevents are the possible causes for the observed variability of the TTSs (Grinin et al. 1991, Herbst et al. 1994,Ismailov 2005 and Herbst et al. 2007). The review of various classification schemes of photometric vari-ability of young stars can be found in the work of Cody et al. (2014). Especially for CTTSs Ismailov (2005)proposed classification scheme based on the light curve shape.Unlike TTSs, the HAEBESs are less photometrically active and less studied. Detailed descriptions of theobserved features of HAEBESs are given in Hillenbrand et al. (1992), Perez & Grady (1997) and Waters &Waelkens (1998). Evidence of stellar winds, jets and mass accretion in the HAEBESs was not found (Waters& Waelkens 1998). The variability (if any) of these stars derives from cool spots and/or from the transit ofdisc clumps. The obscuration events are very likely to be present in most HAEBESs but they can be onlyregistered when the circumstellar disks are located at a small angle to the line of sight (Grinin et al. 1991 andNatta & Whitney 2000). When PMS stars approach the main sequence they lose their distinctive featuresand at this stage they are hardly different from main sequence stars.The stars from our study were selected from the SIMBAD database by exact object types (Variable starof Orion type, Emission line-star, Flare star, and Herbig Ae/Be star) and with the condition on their location − position within 20 arcmin around the well-studied young stellar object V2492 Cyg (see Covey et al. 2011,Aspin 2011, K´osp´al et al. 2013, Hillenbrand et al. 2013, Giannini et al. 2018 and Ibryamov et al. 2018).Photometric observations, especially concerning the long-term behavior of the stars from our study aremissing in the literature. Long-term photometric observations are important for the exact classification ofPMS stars. Such observations are directed at the active star-formation fields with the goal of finding andclassifying the variability of the young stellar objects (YSOs) embedded in them.The present paper is a part of our program for the photometric study of PMS stars located in the NGC7000/IC 5070 star-forming complex. The results from our recent studies have been published in Ibryamovet al. (2015), Ibryamov & Semkov (2016), Semkov et al. (2017) and Ibryamov et al. (2018). Section 2 in thepresent paper gives information about the process of acquiring photometric observations and data reduction.Section 3 describes the obtained results and their analysis. ong-term BV RI light curves of 15 PMS stars in the Pelican Nebula 3
The CCD observations reported in the paper were collected during the time period from 2010 Septemberto 2017 October. All CCD observations were obtained with two telescopes − the 50/70-cm Schmidt andthe 60-cm Cassegrain − administered by the Rozhen National Astronomical Observatory in Bulgaria. Thenumber of observational nights used to estimate the brightness of each object is 119.The observations were performed with two different types of CCD cameras − FLI PL16803 (4096 × × µm/ pixel size) on the 50/70-cm Schmidt telescope and FLI PL09000 (3056 × × µm/ pixel size) on the 60-cm Cassegrain telescope. All frames were takenthrough a standard Johnson − Cousins (
BV RI ) set of filters. The frames are dark frame subtracted and flatfield corrected. The photometric data were reduced using
IDL based
DAOPHOT subroutine. As a reference,the
BV RI comparison sequence of eleven stars in the field around V2492 Cyg reported in Ibryamov etal. (2018) was used. All data were analyzed using the same aperture, which was chosen to have a 4 arcsecradius, while the background annulus was taken from 9 to 14 arcsec. The mean value of the errors in thereported magnitudes is 0.01 − I - and R -band data and 0.01 − V - and B -band data. The stars from our study are listed in Table 1 in the order of rising right ascension. Star identifiers used in thispaper are marked in boldface. Fig. 1 shows an image of the field around V2492 Cyg, where the positions ofthe objects are marked. The registered during our photometric monitoring minimal and maximal magnitudesand the amplitudes of variability in the
BV RI -bands of the stars are given in Table 2.The V magnitude range versus average brightness in the V -band of the investigated objects is shown inFig. 2 (left). The used object designations are as in Table 1. It is seen from the figure, that there is no apparentcorrelation between range and average brightness among the objects. The histogram of V magnitude rangesfor the objects is shown in Fig. 2 (right). Roughly all objects (12) exhibit amplitude of variability on thelong-term in the range between 0.1 and 0.8 mag. The lowest amplitude star is LkH α
168 ( ∆ V = 0.16 mag).Only 3 stars have an amplitude of variability larger than 1 mag. They are LkH α ∆ V = 1.62 mag).We used the 2MASS ( JHK s ) magnitudes of the stars from our study to construct the two − color dia-gram ( J − H / H − K s ) to identify the stars with infrared excess, indicating the presence of disks aroundthem. Fig. 3 shows the location of the main sequence (the dark line) and the giant stars (the green line)from Bessell & Brett (1988), and the CTTSs location (the orange line) from Meyer et al. (1997). A correc-tion to the 2MASS photometric system was performed following the prescription of Carpenter (2001). Thethree parallel dotted lines show the direction of the interstellar reddening vectors determined for the NGC7000/IC 5070 star-forming complex by Straizˇys et al. (2008). On Fig. 3 the objects are designated usingtheir numbers given in Table 1. S. Ibryamov, E. Semkov, T. Milanov & S. Peneva
Table 1: Designations and coordinates of the stars from our study.
Nr GCVS HBC [KW97] LkH α RA J . Dec J . J20503703+4418247 20 50 37.03 +44 18 24.72
J20504608+4419100
20 50 46.08 +44 19 10.13
V1956 Cyg
J20505014+4357536 20 50 50.14 +43 57 53.74 702 50-22
J20505257+4416441 20 50 52.57 +44 16 44.25
V1490 Cyg
J20505357+4421008 20 50 53.58 +44 21 00.96
V1532 Cyg
703 143 J20505378+4421185 20 50 53.78 +44 21 18.57
V1597 Cyg
J20505838+4414444 20 50 58.38 +44 14 44.48 704 50-29
J20510157+4415420 20 51 01.57 +44 15 42.19 705 50-30
J20510271+4349318 20 51 02.71 +43 49 31.910
V1598 Cyg
J20510393+4411406 20 51 03.93 +44 11 40.611
V1492 Cyg
J20510570+4416322 20 51 05.70 +44 16 32.312 714 50-53
J20514191+4416082 20 51 41.91 +44 16 08.213 717 51-4
J20520604+4417160 20 52 06.05 +44 17 16.114 298 51-15
J20522676+4417066 20 52 26.76 +44 17 06.615 51-16
J20522740+4403259 20 52 27.40 +44 03 25.9
References: General Catalogue of Variable Stars (Samus et al. 2017); Herbig & Bell (1988); Kohoutek &Wehmeyer (1997); Herbig (1958); Note:
Star identifiers used in this paper are marked in boldface.
Using data from our multicolor photometry we constructed three color − magnitude diagrams ( B − V / V , V − R / V and V − I / V ) of the objects, which are displayed in Fig. A.1. For all objects we made time-seriesanalysis for a periodicity search with the software package PERIOD
04 (Lenz & Breger 2005). In the presentpaper we discuss the stars in groups with close photometric behaviors and features. α α
146 and V1492 Cyg
Unlike the other stars studied in the paper, during our photometric monitoring LkH α α
146 and V1492 Cyg show bigger amplitudes of the photometric variability. These objects are included inthe list of candidates for YSOs published by Guieu et al. (2009).The spectrogram of LkH α
137 taken by Herbig (1958) shows bright H β and H γ on a continuous spec-trum too weak for classification. According to the author of direct photographs, the image of LkH α
137 isdiffuse, as if it were closely nebulous. Ogura et al. (2002) detected H α emission in the spectrum of V1490Cyg. The light curves of LkH α α
146 and V1492 Cyg constructed on the basis of ourobservations are plotted on Fig. 4.It can be seen from Fig. 4 that LkH α
137 spends most of the time at high light. During our photometricmonitoring, one decline in the star’s brightness is registered. The observed drop began in mid-2012 and itreached the biggest depth in 2013 April with amplitude 1.40 mag in B -band, 1.18 mag in V -band, 1.01 magin R -band and 0.70 mag in I -band. In 2013 May the star’s brightness returned to the previous high level. ong-term BV RI light curves of 15 PMS stars in the Pelican Nebula 5
Fig. 1: An image of the field around V2492 Cyg obtained on 2013 September 5 in R -band with the 50/70-cmSchmidt telescope at Rozhen NAO. The stars from our study and V2492 Cyg are marked.Table 2: The registered minimal and maximal magnitudes and the amplitudes of variability in the BV RI -bands of the stars from our study.
Nr Star B min B max V min V max R min R max I min I max ∆ B ∆ V ∆ R ∆ I α
137 18.53 17.13 16.64 15.46 15.26 14.25 13.65 12.95 1.40 1.18 1.01 0.702 J2050+4419 19.35 18.86 17.64 17.24 16.35 15.94 14.83 14.48 0.49 0.40 0.41 0.353 V1956 Cyg 17.46 17.25 16.26 16.09 15.45 15.25 14.47 14.27 0.21 0.17 0.20 0.204 LkH α
141 17.34 17.02 15.79 15.46 14.90 14.46 13.93 13.46 0.32 0.33 0.44 0.475 V1490 Cyg 18.14 16.99 16.84 15.40 15.69 14.40 14.53 13.29 1.15 1.44 1.29 1.246 V1532 Cyg 18.56 17.78 16.80 16.14 15.44 14.91 13.87 13.51 0.78 0.66 0.53 0.367 V1597 Cyg 18.07 17.71 16.34 15.99 15.17 14.76 13.65 13.29 0.36 0.35 0.41 0.368 LkH α
146 18.32 17.58 16.67 15.91 15.58 14.78 14.37 13.68 0.74 0.76 0.80 0.699 LkH α
147 15.99 15.84 14.56 14.35 13.47 13.29 12.21 12.04 0.15 0.21 0.18 0.1710 V1598 Cyg 15.27 14.97 14.28 14.01 13.69 13.43 13.13 12.87 0.30 0.27 0.26 0.2611 V1492 Cyg 17.85 16.90 16.93 15.31 15.68 14.16 14.59 13.14 0.95 1.62 1.52 1.4512 LkH α
161 18.63 17.97 17.13 16.48 15.89 15.39 14.69 14.29 0.66 0.65 0.50 0.4013 LkH α
168 14.87 14.75 13.60 13.44 12.78 12.57 11.81 11.68 0.12 0.16 0.21 0.1314 LkH α
172 16.19 16.02 14.76 14.54 13.82 13.59 12.83 12.69 0.17 0.22 0.23 0.1415 LkH α
173 - - 17.61 17.19 17.00 16.62 13.46 13.30 - 0.42 0.38 0.16
S. Ibryamov, E. Semkov, T. Milanov & S. Peneva
13 14 15 16 17 18Average V mag.0.00.51.01.52.0 R ange i n V m ag . N u m be r o f s t a r s Fig. 2: Left: Range in V versus average V mag for stars from our study; Right: Histogram of V mag rangesfor stars from our study. s J - H
15 131282 14941310 7 6 115
Fig. 3: The J − H versus H − K s diagram for the stars from our study detected in the three bands in 2MASScatalogue.The measured color indices ( V − I , V − R and B − V ) versus the star’s V magnitude are plottedon Fig. A.1. It can be seen from Fig. A.1 that LkH α
137 becomes redder as it fades. Normally the starbecomes redder when its light is being obscured by dust clumps or filaments in the line of sight. On the2MASS color − color diagram (Fig. 3) LkH α
137 lies close to the CTTSs location, i.e. the star has infraredexcess indicating the presence of disk around it. Therefore, the probable cause for the observed drop in thebrightness of LkH α
137 is the variation in the density of the dust in orbit around the star, which crosses theline of sight and obscures the object. Evidence of periodicity in the brightness variability of LkH α
137 isnot detected. ong-term
BV RI light curves of 15 PMS stars in the Pelican Nebula 7 M agn i t ude s IRVB
LkHá 137 55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 201813141516171819 M agn i t ude s IRVB
V1490 Cyg55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 201813141516171819 M agn i t ude s IRVB
LkHá 146 55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 20181213141516171819 M agn i t ude s IRVB
V1492 Cyg
Fig. 4: Multicolor light curves of LkH α α
146 and V1492 Cyg.V1490 Cyg and V1492 Cyg also spend most of the time at high light (Fig. 4). The stars exhibit irreg-ular multiple fading events in all bands with different amplitudes. The time periods of the declines in thebrightness are relatively short, usually we have only one photometric point in some minima. The registeredamplitudes of the brightness variations of V1490 Cyg and V1492 Cyg during the whole time of observa-tions are given in Table 2. On the 2MASS diagram (Fig. 3) V1490 Cyg and V1492 Cyg are located closeto the CTTSs line. The measured color indices versus the stellar V magnitude for the objects are plotted onFig. A.1. It is seen from the figure that the stars become redder as they fade. Such color variations are typi-cal for T Tauri variables, whose variability is produced by small irregular obscuration by the circumstellarmaterial or by the rotational modulation of one or more spots on the stellar surface. Evidence of periodicityin the brightness variability of V1490 Cyg and V1492 Cyg is not detected.LkH α
146 shows both active states with high amplitude and quiet states with lower amplitude, at thesame brightness level. The registered amplitudes of the brightness variations of the star during our photo-metric monitoring are given in Table 2. An important result from our study of LkH α
146 is the registeredpreviously unknown periodicity in its photometric behavior. On Fig. 5 we show the obtained periodogramusing all data in R -band of the star. We found a significant peak in the periodogram corresponding to 7.365day period. False Alarm Probability estimation was done by randomly deleting about 10% of the data forabout 20 times and then returning the period of determination. The period remain stable during the wholetime of our observations (2010 − α
146 in the R -band according to 7.365 day period is also plotted on Fig. 5. S. Ibryamov, E. Semkov, T. Milanov & S. Peneva -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2Phase14.614.815.015.215.415.615.8 R [ m ag ] P o w e r . d Fig. 5: Periodogram of the photometric data of LkH α α In the literature these objects were reported as flare stars. 2MASS J20504608+4419100 was discoveredand classified as a flare star by Jankovics et al. (1980). The authors reported a flare event on 1979August 28 when the brightness of the star increased with an amplitude of 3.2 mag in U -light. Erastova& Tsvetkov (1974) reported a flare event on 1973 August 24 in V1597 Cyg when the star’s brightnessincreased with an amplitude of 3.0 mag in U -light. Tsvetkov et al. (1974) registered a flare event on1972 August 16 in the photometric behavior of V1598 Cyg with an amplitude of 1.7 in U -light. Rosinoet al. (1987) also reported a flare event in V1598 Cyg on 1972 October 5 with an amplitude of 2.6 in U -light. K´osp´al et al. (2011) used V1598 Cyg as one of the comparison stars in their study of VSXJ205126.1+440523 (V2492 Cyg). V1956 Cyg was classified as a flare star by Tsvetkov & Tsvetkova (1990).During our photometric monitoring we did not register flare events in these stars. Our negative resultdoes not mean that these objects do not show flares. Our mode of observations (about 100 estimations for ∼ BV RI light curves of 2MASS J20504608+4419100, V1597 Cyg, V1598 Cyg and V1956 Cyg areplotted on Fig. 6. The registered amplitudes of variability of the stars are given in Table 2. It can be seenthat these objects show no significant photometric variability. On the 2MASS diagram (Fig. 3) the objectsare located in different areas − ong-term BV RI light curves of 15 PMS stars in the Pelican Nebula 9 M agn i t ude s IRVB M agn i t ude s IRVB
V1597 Cyg55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 2018131415 M agn i t ude s IRVB
V1598 Cyg 55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 20181415161718 M agn i t ude s IRVB
V1956 Cyg
Fig. 6: Multicolor light curves of 2MASS J20504608+4419100, V1597 Cyg, V1598 Cyg and V1956 Cyg.It is possible V1598 Cyg and V1956 Cyg to be projecting stars on the front of the field of NGC 7000/IC5070 complex. Using the data from our photometric observations it is very difficult to classify these stars.Evidence of periodicity in their brightness variability is not detected. α α α
172 and LkH α These objects are included in the list of H α emission-line stars published by Herbig (1958). Guieu etal. (2009) included these stars in their list of YSO candidates. The spectrogram of LkH α
172 taken byHerbig (1958) shows an absorption spectrum of intermediate or late G type, with rather a strong emissionat H β . According to the author emission may also be present at H γ . Terranegra et al. (1994) determined thespectral type of LkH α
172 as G3 III.The results from our photometric monitoring indicate that LkH α α α α
173 show photometric variability with small amplitudes. The registered amplitudes of variabilityof the stars from the current section are given in Table 2.
BV RI light curves of LkH α α α
172 and LkH α
173 are plotted on Fig. 7. On the 2MASS color − color diagram (Fig. 3)the objects are located close to the CTTSs line. These stars have infrared excess indicating the presence ofcircumstellar disks around them. Probably the brightness variability of the objects is caused by the variationsin the mass accretion rate and/or the modulation of the stellar brightness in the presence of spot(s) onthe stellar surface. The registered amplitudes of photometric variability also confirmed this suspicion (seeHerbst et al. 1994). Evidence of periodicity in the brightness variability of the stars is not detected. M agn i t ude s IRVB
LkHá 141 55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 201813141516171819 M agn i t ude s IRVB
V1532 Cyg55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 2018141516171819 M agn i t ude s IRVB
LkHá 161 55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 2018121314151617 M agn i t ude s IRVB
LkHá 17255500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 20181617181314 M agn i t ude s IRV
LkHá 173
Fig. 7: Multicolor light curves of LkH α α α
172 and LkH α α
147 and LkH α In the literature LkH α
147 and LkH α
168 are classified as HAEBESs. The spectrogram of LkH α
147 takenin 1957 by Herbig (1958) shows an essentially continuous spectrum with emission at H β . According to theauthor although no definite spectral type can be assigned, there is no doubt that this is an early-type star.Hern´andez et al. (2004) classified LkH α
147 as a HAEBES and estimated its spectral type as B2. Herbst& Shevchenko (1999) included the star in their list of HAEBES and measured V =14.45 mag, B − V =1.50mag and V − R =1.61 mag of the object during the time period 2450007 − ong-term BV RI light curves of 15 PMS stars in the Pelican Nebula 11 M agn i t ude s IRVB
LkHá 147 55500 56000 56500 57000 57500 58000J.D. (24...)2010 2011 2012 2013 2014 2015 2016 2017 20181112131415 M agn i t ude s IRVB
LkHá 168
Fig. 8: Multicolor light curves of LkH α
147 and LkH α α
168 is intermediate or late B, with no emissionapparent in the photographic region on a 1954 plate. Chavarr´ıa-K. et al. (1989) concluded the spectral typeof the star is F8-G0. According to the authors LkH α
168 has a warm circumstellar dust envelope of ∼ α
168 as A8-F2e. Herbst & Shevchenko (1999) included the star in their list of HAEBES and measured V =13.48 mag, U − B =1.05 mag, B − V =1.25 mag, and V − R =1.21 mag of the object during the timeperiod 2446255 − BV RI light curves of LkH α
147 and LkH α
168 are plotted on Fig. 8. During our photometric moni-toring these objects show no significant photometric variability. We registered V =14.44 mag, B − V =1.46mag, V − R =1.06, and V − I =2.31 mag for LkH α V =13.54 mag, B − V =1.28 mag, V − R =0.84,and V − I =1.79 mag for LkH α α
147 and LkH α
168 are very close to estimationsfrom work of Herbst & Shevchenko (1999). There is only a significant difference in V − R values forthe two stars. Probably the reason for this distinction that the V − R color index is in the Johnson systemin work of Herbst & Shevchenko (1999), and it is in the Cousins system in the present paper. We usedthe transformation described in Fernie (1983) and we obtained for V − R color index from the work ofHerbst & Shevchenko (1999) the value 1.06 mag for LkH α
147 and 0.85 mag for LkH α V − R color index after the transformation coincide with ones in present paper.On the 2MASS diagram (Fig. 3) LkH α
147 is located close to the main sequence line while LkH α We reported for the
BV RI photometric behavior of 15 PMS stars around V2492 Cyg in the IC 5070 star-forming region. Our observations cover 7-year time span (2010 − α α
146 and V1492 Cyg show bigger amplitudes of photometric variabilityamong the objects from our study. The results indicate that probably these stars are CTTSs; (ii) although2MASS J20504608+4419100, V1597 Cyg, V1598 Cyg and V1956 Cyg were classified as flare stars in theliterature, we did not register any such events. Our negative result does not mean that these objects do notshow flares; (iii) during our photometric monitoring LkH α α α α α
172 and LkH α
173 show no significant photometric variability; (iv) for LkH α
146 we identifieda 7.365 d rotational periodicity in its photometric behavior.Further both photometric and spectral observations would offer clearer insight into the physical natureof the objects from our study.
Acknowledgements
This research has made use of the NASA’s Astrophysics Data System. This pub-lication makes use of data products from the Two Micron All Sky Survey, which is a joint project ofthe University of Massachusetts and the Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administration and the National ScienceFoundation. This study has made use of the SIMBAD database (Wenger et al. 2000) and the VizieR cat-alogue access tool (Ochsenbein et al. 2000), operated at CDS, Strasbourg, France. This work was partlysupported by the National Science Fund of the Ministry of Education and Science of Bulgaria under grantsDM 08-2/2016, DN 08-1/2016, DN 08-20/2016 and DN 18-13/2017 and by funds of the project RD-08-112/2018 of the University of Shumen.
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Appendix A: COLOR INDICES ( V − I , V − R AND B − V ) VERSUS THE STELLAR V -MAGNITUDE OF THE STARS FROM OUR STUDY This manuscript was prepared with the RAA L A TEX macro v1.2. V V-IV-RB-V
LkHá 137 1.0 1.2 1.4 1.6 1.8 2.0 2.6 2.8 3.0Color index1.0 1.2 1.4 1.6 1.8 2.0 2.6 2.8 3.017.217.317.417.517.617.7 V V-IV-RB-V V V-IV-RB-V
V1956 Cyg0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4Color index0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.415.515.615.715.8 V V-IV-RB-V
LkHá 141 0.8 1.0 1.2 1.6 2.2 2.4 2.6Color index0.8 1.0 1.2 1.6 2.2 2.4 2.615.215.616.016.416.8 V V-IV-RB-V
V1490 Cyg 1.0 1.2 1.4 1.6 1.8 2.0 2.6 2.8 3.0Color index1.0 1.2 1.4 1.6 1.8 2.0 2.6 2.8 3.016.216.416.616.8 V V-IV-RB-V
V1532 Cyg1.0 1.2 1.4 1.6 1.8 2.0 2.6 2.8 3.0Color index1.0 1.2 1.4 1.6 1.8 2.0 2.6 2.8 3.016.016.116.216.316.4 V V-IV-RB-V
V1597 Cyg 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6Color index0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.615.816.016.216.416.6 V V-IV-RB-V
LkHá 146 1.0 1.2 1.4 1.6 2.2 2.4 2.6Color index1.0 1.2 1.4 1.6 2.2 2.4 2.614.414.5 V V-IV-RB-V
LkHá 1470.6 1.0 1.2Color index0.6 1.0 1.214.014.114.214.3 V V-IV-RB-V
V1598 Cyg 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8Color index0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.815.215.616.016.416.8 V V-IV-RB-V
V1492 Cyg 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6Color index0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.616.416.616.817.017.2 V V-IV-RB-V
LkHá 1610.8 1.0 1.2 1.4 1.8 2.0Color index0.8 1.0 1.2 1.4 1.8 2.013.513.6 V V-IV-RB-V
LkHá 168 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2Color index0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.214.514.614.7 V V-IV-RB-V
LkHá 172 0.4 0.8 4.0Color index0.4 0.8 4.017.217.317.417.517.6 V V-IV-R
LkHá 173